title: Is cystatin C a better marker than creatinine for evaluating residual renal function in patients on continuous ambulatory peritoneal dialysis?
abstract: BACKGROUND
  Current clinical assessments of residual renal function (RRF) for continuous ambulatory peritoneal dialysis (CAPD) patients usually require 24 h of urine collection, which is sometimes difficult for patients and contributes to random errors. Objective. Our study aims to investigate whether serum cystatin C (CysC) can serve as a better marker of RRF than serum creatinine (Cr) in CAPD and to develop a formula to estimate RRF with CysC levels.
  
  
  METHODS
  One hundred and sixty CAPD patients from a single dialysis unit were randomly divided into modeling (n(1) = 120) and validation (n(2) = 40) groups. RRF was assessed as the average of the renal clearances of urea and creatinine. We then derived RRF formulas based on the CysC and Cr levels from the modeling group and validated them by comparison with a published CysC-based equation and Modification of Diet in Renal Disease formula.
  
  
  RESULTS
  CysC levels were inversely related to RRF, Kt/V(urea) and total weekly Ccr but were unrelated to age, gender, body mass index, diabetes or peritoneal clearance. The RRF formulas derived from CysC and Cr were (sinh(ln(6.736-0.566 CysC)))(2) and (sinh(ln(6.097-0.265 Cr)))(2), respectively. When applied to the validation group, the estimated RRF based on CysC (2.8 ± 1.2 mL/min/1.73 m(2)) was similar to that of on Cr (2.8 ± 1.3 mL/min/1.73 m(2)) and the measured RRF (2.9 ± 1.7 mL/min/1.73 m(2)). The CysC formula showed a small bias, with the best 30 and 50% accuracy and had a larger area under the curve and higher sensitivity and specificity when compared to the Cr formula and other formulas.
  
  
  CONCLUSIONS
  Serum CysC may be a good marker for the estimation of RRF in CAPD patients. The derived CysC formula may be used to reliably estimate RRF in CAPD patients without the need for collection of 24 h urine.
authors.affiliation: Department of Nephrology, Sun Yat-sen University, Guangzhou, China.
authors.forename: Qiongqiong
authors.initials: Q
authors.lastname: Yang
authors.forename: Ruixi
authors.initials: R
authors.lastname: Li
authors.forename: Zhewen
authors.initials: Z
authors.lastname: Zhong
authors.forename: Haiping
authors.initials: H
authors.lastname: Mao
authors.forename: Jinjin
authors.initials: J
authors.lastname: Fan
authors.forename: Jianxiong
authors.initials: J
authors.lastname: Lin
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.forename: Xueqin
authors.initials: X
authors.lastname: Wang
authors.forename: Zhibin
authors.initials: Z
authors.lastname: Li
authors.forename: Xueqing
authors.initials: X
authors.lastname: Yu
mesh_terms: D000465:Algorithms; D015415:Biomarkers / Q000097:blood*; D015992:Body Mass Index; D003404:Creatinine / Q000097:blood*; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007674:Kidney Diseases / Q000097:blood* / Q000628:therapy*; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D010531:Peritoneal Dialysis, Continuous Ambulatory; D012372:ROC Curve; D012680:Sensitivity and Specificity; D059349:Urine Specimen Collection
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D003404:Creatinine